1. Field of the Invention
The present invention relates to the field of optical scientific instrumentation. More specifically, the present invention relates to a novel flexure coupled moving mirror utilized in a Fourier-Transform infrared (FTIR) interferometer.
2. Discussion of the Related Art
An optical interferometer used in a scientific analytical instrument relies on the interference of superimposed optical beams as part of the interrogation means. When configured as a Michelson Fourier-Transformed infrared (FTIR) instrument, the optical output of the interferometer is called an interferogram. The FTIR interferometer itself often includes a beamsplitter and two mirrors, one that is conventionally stationary, and one which is conventionally mobile. The mobile mirror moves along the optic axis while staying optically perpendicular to the light beam at all times. The movement of the mobile mirror is often desired to be feedback controlled in order to hold the mirror velocity constant (while also controlling tilt) so that the analytical radiation that passes through the interferometer produces an accurate interferogram. Conventional interferometers have a moving mirror assembly that includes a linear ball bearing, air bearing, slide bearing, or a flexure bearing and is often driven by a linear motor (e.g., a coil coupled to a permanent magnet) to provide velocity control.
Because of the delicate nature of such instruments, conventional systems are often configured to be precisely aligned with mechanical adjustments that must stay correctly adjusted even if the system is shipped around the world. This has resulted in expensive stiff precision mechanical interferometer systems that sometimes need adjustments in the field after shipping shocks has shifted the alignment of the critical flat optical surfaces. In operation, many of such conventional systems use active control systems (i.e., dynamic alignment) to control mirror tilt as the interferometer scans and collects a desired spectral data. Such systems can only operate if the interferometer is scanning under the control of a laser based velocity control servo that all typical scanning interferometers use.
However, it is to be noted that while all practical interferometers use one or more laser based velocity measuring systems to enable a servo control system to control the velocity of the moving mirror, such servos can only correct velocity errors after a small time delay (caused by the velocity measurement process and the delay in generating correcting forces). Therefore velocity errors that occur slowly are corrected and largely eliminated. However velocity errors that occur at a rapidly changing rate due to induced noise cannot be corrected completely leaving a remaining velocity error that negatively affects the spectra data collected. In addition, many interferometers use a laser phase tilt error measuring system to control tilt in both X and Y axis, which in addition to the velocity control servo, also needs to be monitored to correct undesired tilt errors via induced noise, which can additionally affect a given spectra.
Background information on such an interferometer system that utilizes dynamic control of the moving mirror, is described and claimed in, U.S. Pat. No. 5,883,712, entitled, “INTERFEROMETER OF AN INFRARED SPECTROMETER WITH DYNAMIC MOVING MIRROR ALIGNMENT” issued Mar. 16, 1999, to John M. Coffin, including the following, “[i]n accordance with the present invention, an interferometer for an infrared spectrometer provides dynamic alignment of the moving mirror to maintain precise alignment between the moving mirror and the fixed mirror. The alignment of the moving mirror in this manner maximizes the stability of the interferometer while achieving high levels of output accuracy despite vibrations due to the movement of the moving mirror on its bearings and vibrations transmitted from external sources to the interferometer. The dynamics of the mounting of the moving mirror allow the position of the mirror to be controlled with high accuracy even in the presence of relatively high frequency vibrations. The structure of the interferometer and of the detectors and controls for maintaining the alignment of the moving mirror are nonetheless simple in construction and contribute relatively little additional bulk or weight to the interferometer.”
Accordingly, a need exists for an improved inexpensive moving mirror assembly so as to correct tilt and velocity errors at the moving mirror component in addition to simultaneously isolating vibration and noise caused by the imperfections in the bearing surfaces of all rolling and sliding bearings used in interferometers.